HVOF Flame Spray Introduction

The key part of the HOVF equipment is the spray gun, which is consist of firebox(making the spraying material particles fully heated and accelerated), Laval nozzle(accelerating the flame flow into supersonic speed) and constant section long nozzle(making the spraying material particles fully heated and accelerated). It works like this: the liquid entering the firebox by small holes burns, such as the kerosene, lighted after atomization and mixed with oxygen, producing strong gas-phrase reaction, and the heat energy released by burning will make the product expand violently. When the expanded gas flows through Laval nozzle, it will be committed by the nozzle and then form a supersonic high temperature flame flow, which heats and accelerates spray materials to the substrate surface to form high quality coatings.

Supersonic flame uses propane, propylene and other hydrocarbon-based gas or hydrogen and high-pressure oxygen in the combustion chamber, or it becomes high temperature, high speed combustion flame in a special nozzle. The speed of the flame flow can even become more than 5mach(1500m/s). At present, it’s always called HVOF(high velocity oxygen fuel). The powder is fed axially into the flame, which can be heated in a molten or semi-molten status and speed up to 300-500m/s or even higher to obtain a high strength, dense and good quality coating. Supersonic flame has a high speed but a relatively low temperature, 3000℃ approximately. As for WC-Co based cemented carbide, it can effectively inhibit the decomposition of WC during spray process. The coating is not only with high bonding strength and densification, but also has excellent wear resistance, and its wear resistance greatly exceeding the plasma coating, equivalent to explosion spray coating, and also beyond hard chrome layer and spray melting layer. The applications are extremely extensive.

Wisdom mainly thermal spray powders used for HVOF are as follows: 88WC-12Co,

83WC-17Co ,

90WC-10Ni ,

WC-10Co-4Cr,

Ni60(A), etc.